Note for Ground Improvement Techniques - GIT By TPO Department

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Ground Improvement Techniques for Stabilization of Soil
for Various Purposes
GOPAL MISHRA DEC 8, 2016
The ground can be improved by adapting certain ground
improvement techniques. Vibro-compaction increases the
density of the soil by using powerful depth vibrators. Vacuum
consolidation is used for improving soft soils by using a
vacuum pump.
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Vibro Compaction
Vacuum Consolidation
Preloading of soil
Soil stabilization by heating or vitrification
Ground freezing
Vibro-replacement stone columns
Mechanically stabilized earth structures
Soil nailing
Micro-piles
Grouting
Vibro-Compaction Method of Ground Improvement
Preloading method is used to remove pore water over time.
Heating is used to form a crystalline or glass product by
electric current. Ground freezing converts pore water to ice to
increase their combined strength and make them impervious.
Vibro-replacement stone columns improve the bearing
capacity of soil whereas Vibro displacement method displaces
the soil. Electro osmosis makes water flow through fine
grained soils.
Electro kinetic stabilization is the application of electro
osmosis. Reinforced soil steel is used for retaining structures,
sloping walls, dams etc. seismic loading is suited for
construction in seismically active regions. Mechanically
stabilized earth structures create a reinforced soil mass.
Vibro-compaction, sometimes referred to as Vibroflotation, is
the rearrangement of soil particles into a denser configuration
by the use of powerful depth vibration.Vibro Compaction is a
ground improvement process for densifying loose sands to
create stable foundation soils.
The principle behind vibro compaction is simple. The
combined action of vibration and water saturation by jetting
rearranges loose sand grains into a more compact state. Vibro
Compaction is performed with specially-designed vibrating
probes. Both horizontal and vertical modes of vibration have
been used in the past.
The geo methods like Geosynthetics, Geogrid etc. are
discussed. Soil nailing increases the shear strength of the insitu soil and restrains its displacement. Micro pile gives the
structural support and used for repair/replacement of existing
foundations.
Grouting is injection of pumpable materials to increase its
rigidity. The jet grouting is quite advanced in speed as well as
techniques when compared with the general grouting.
Rapid urban and industrial growth demands more land for
further development. In order to meet this demand land
reclamation and utilization of unsuitable and environmentally
affected lands have been taken up. These, hitherto useless
lands for construction have been converted to be useful ones
by adopting one or more ground improvement techniques. The
field of ground improvement techniques has been recognized
as an important and rapidly expanding one.
Latest Ground Improvement Techniques
Following are the recent methods of ground improvement
Techniques used for stabilization of soil:
The vibrators used by Terra Systems consist of torpedo-shaped
probes 12 to 16 inches in diameter which vibrates at
frequencies typically in the range of 30 to 50 Hz. The probe is
first inserted into the ground by both jetting and vibration.
After the probe reaches the required depth of compaction,
granular material, usually sand, is added from the ground
surface to fill the void space created by the vibrator. A
compacted radial zone of granular material is created
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Advantages of Vibro Compaction Method:
Reduction of foundation settlements.
Reduction of risk of liquefaction due to seismic activity.
Permit construction on granular fills.
Vacuum Consolidation of Soil for Ground Improvement

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Vacuum Consolidation is an effective means for improvement
of saturated soft soils. The soil site is covered with an airtight
membrane and vacuum is created underneath it by using dual
venture and vacuum pump. The technology can provide an
equivalent pre-loading of about 4.5m high conventional
surcharge fill. Vacuum-assisted consolidation preloads the soil
by reducing the pore pressure while maintaining a constant
total stress.
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Applications of Vacuum Consolidation of Soil:
Replace standard preloading techniques eliminating the risk of
failure.
Combine with a water preloading in scare fill area. The
method is used to build large developments on thick
compressible soil.
Combine with embankment pre-load using the increased
stability
Preloading or Pre-Compression of Soil for Ground
Improvement
Preloading has been used for many years without change in
the method or application to improve soil properties.
Preloading or pre-compression is the process of placing
additional vertical stress on a compressible soil to remove pore
water over time. The pore water dissipation reduces the total
volume causing settlement. Surcharging is an economical
method for ground improvement. However, the consolidation
of the soils is time dependent, delaying construction projects
making it a non-feasible alternative.
Heating or vitrification breaks the soil particle down to form a
crystalline or glass product. It uses electrical current to heat
the soil and modify the physical characteristics of the soil.
Heating soils permanently alters the properties of the soil.
Depending on the soil, temperatures can range between 300
and 1000 degree Celsius. The impact on adjacent structures
and utilities should be considered when heating is used. .
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The soils treated are Organic silt, Varved silts and clays, soft
clay, Dredged material The design considerations which
should be made are bearing capacity, Slope stability, Degree
of consolidation.
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Applications of Preloading of Soil
Reduce post-construction
Settlement
Reduce secondary compression.
Densification
Improve bearing capacity
Thermal Stabilization of Soil for Ground Improvement
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Applications of Vitrification of Soil:
Immobilization of radioactive or contaminated soil
Densification and stabilization
Ground Freezing Technique for Ground Improvement
Ground freezing is the use of refrigeration to convert in-situ
pore water to ice. The ice then acts as a cement or glue,
bonding together adjacent particles of soil or blocks of rock to
increase their combined strength and make them
impervious. The ground freezing considerations
are Thermal analysis, Refrigeration system
geometry, Thermal properties of soil and rock, freezing rates,
Energy requirements, Coolant/ refrigerant distribution system
analysis.
Applications of Ground Freezing Technique
Temporary underpinning
Temporary support for an excavation
Prevention of groundwater flow into excavated area
Temporary slope stabilization
Temporary containment of toxic/hazardous waste
contamination
Vibro-Replacement Stone Columns for Ground
Improvement

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Principles of Mechanically Stabilized Earth Structures:
The reinforcement is placed in horizontal layers between
successive layers of granular soil backfill. Each layer of
backfill consists of one or more compacted lifts.
A free draining, non plastic backfill soil is required to ensure
adequate performance of the wall system.
For walls reinforced with metallic strips, load is transferred
from the backfill soil to the strip reinforcement by shear along
the interface.
For walls with ribbed strips, bar mats, or grid reinforcement,
load is similarly transferred but an additional component of
strength is obtained through the passive resistance on the
transverse members of the reinforcement.
Facing panels are typically square, rectangular, hexagonal or
cruciform in shape and are up to 4.5m ^2 in area.
MSEW- Mechanically Stabilized Earth Walls, when the face
batter is generally steeper than 70 degrees.
RSS- Reinforced Soil Slopes, when the face batter is
shallower.
Applications of Mechanically Stabilized Earth Structures:
RSS structures are cost effective alternatives for new
construction where the cost of embankment fill, right-of-way,
and other consideration may make a steeper slope desirable.
Another use of reinforcement in engineered slopes is to
improve compaction at the edges of a slope to decrease the
tendency for surface sloughing.
Design:
Current practice consists of determining the geometric
reinforcement to prevent internal and external failure using
limit equilibrium of analysis.
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Soil Nailing Technique for Ground Improvement
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The fundamental concept of soil nailing consists of reinforcing
the ground by passive inclusions, closely spaced, to create insitu soil and restrain its displacements. The basic design
consists of transferring the resisting tensile forces generated in
the inclusions into the ground through the friction mobilized at
the interfaces.
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Applications of Soil Nailing Technique:
Stabilization of railroad and highway cut slopes
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Excavation retaining structures in urban areas for high-rise
building and underground facilities
Tunnel portals in steep and unstable stratified slopes
Construction and retrofitting of bridge abutments with
complex boundaries involving wall support under piled
foundations
Micropiles for Ground Improvement
Micropiles are small diameter piles (up to 300 mm), with the
capability of sustaining high loads (compressive loads of over
5000 KN).The drilling equipment and methods allows
micropiles to be drilled through virtually every ground
conditions, natural and artificial, with minimal vibration,
disturbances and noise, at any angle below horizontal. The
equipment can be further adapted to operate in locations with
low headroom and severely restricted access.
Applications of Micropiles for Ground Improvement
For Structural Support and stability
Foundation for new structures
Repair / Replacement of existing foundations
Arresting / Prevention of movement
Embankment, slope and landslide stabilization
Soil strengthening and protection
Example of Micro Piles for Ground Improvement:
In India, in some circumstances steel pipes, coated wooden
piles are used as cost-effective Options in improving the
bearing capacity of foundation or restrict Displacements to
tolerable levels and similar uses in stabilization of slopes,
strengthening of foundations are common.
Sridharan and Murthy (1993) described a Case study in which
a ten-storeyed building, originally in a precarious condition
due To differential settlement, was restored to safety using
micropiles. Galvanized steel Pipes of 100 mm diameter and 10
m long with bottom end closed with shoe, driven at An angle
of 60o with the horizontal were used and the friction between
the pile and the soil was used as the design basis in evolving
the remedial measures.
General Grouting for Ground Improvement
Grouting is the injection of pumpable materials into a soil or
rock formation to change the physical characteristics of the
formation. Grouting selection considerations are Site
specific requirement, Soil type, Soil groutability,
Porosity. Grouting can be prevented by Collapse of granular
soils, Settlement under adjacent foundations, Utilities damage,